Data Transfer Tools: bbcp

This article provides information about the bbcp data transfer tool. In particular:

  • what is bbcp?
  • using bbcp on JASMIN.
  • configuring bbcp for JASMIN.
  • tuning recommendations for bbcp.
  • trouble-shooting bbcp problems.

What is bbcp?

bbcp is a simple command-line tool which can use your SSH connection to transfer data in and out of JASMIN efficiently. It works in a similar way to GridFTP over SSH in that it connects to the transfer server using your usual SSH credentials but then can set up parallel data streams for transferring data. One advantage of bbcp that it is provided as a single binary executable which is easy to download and use.

Using bbcp on JASMIN

The  bbcp command is installed on the JASMIN transfer servers jasmin-xfer1.ceda.ac.ukcems-xfer1.cems.rl.ac.uk and the high-performance data transfer server (jasmin-xfer2.ceda.ac.uk). Check with your local administrator to see if it is installed centrally on your own system. If it isn't, you may need to download the correct binary from the bbcp download site. This can be done as an unprivileged user. Once you have the bbcp command you can access any file which is readable by you when logged into JASMIN, or write to a Group Workspace that you have access to.

Configuring bbcp for JASMIN

When contacting  jasmin-xfer1.ceda.ac.uk you will need to set a couple of important options for it to work. The exact options depend on whether you are moving data into or out of JASMIN, and from where the transfer is initiated.

The  bbcp protocol, in common with most high-bandwidth transfer tools, requires a set of ports to be open at one or both ends in order to establish data connections. Due to firewall restrictions this range of ports needs to be agreed in advance. In the case of jasmin-xfer1.ceda.ac.uk the range of ports is 50000:51000. Therefore all bbcp commands must contain the option --port 50000:51000.

Also,  jasmin-xfer1 will only allow incoming connections on these ports, therefore jasmin-xfer1 must be the server which listens for data connections. By default bbcp will listen for data connections at the end receiving data and connect from the end sending data. Therefore, with the default options, bbcp will succeed when pushing data to jasmin-xfer1 but fail when pulling data from it. In order to pull data, with the transfer initiated on the remote server, you must include the -z flag. Therefore the recommended commands for transferring in either direction are:

Initiate on JASMIN: Pull Data from remote server

[user@jasmin-xfer1]$ bbcp -v -4 -P 5 -F --port 50000:51000 username@remote-server:<PATH-TO-SOURCE-FILE> <PATH-TO-TARGET-FILE>

Initiate on JASMIN: Push Data

[user@jasmin-xfer1]$ bbcp -v -4 -P 5 --port 50000:51000 <PATH-TO-SOURCE-FILE> username@remote-server:<PATH-TO-TARGET-FILE>

Initiate on remote server: Pull Data from JASMIN

[user@remote-server]$ bbcp -v -z -4 -P 5 --port 50000:51000 username@jasmin-xfer1.ceda.ac.uk:<PATH-TO-SOURCE-FILE> <PATH-TO-TARGET-FILE>

Initiate on remote server: Push Data to JASMIN

[user@remote-server]$ bbcp -v -4 -P 5 -F --port 50000:51000 <PATH-TO-SOURCE-FILE> username@jasmin-xfer1.ceda.ac.uk:<PATH-TO-TARGET-FILE>

In this case the "-v"  flag produces verbose output ."-V" can be used for even more verbose output. The "-4" option forces use of IP version 4 instead of IPv6 (essential for transfers to and from jasmin-xfer1 or other JASMIN hosts), and the "-P <n>" option reports the status of the transfer every n seconds.  The default behaviour will print nothing. The "-F" option skips a check on the target host to check if there is enough disk space. This overcomes occasional problems where free space is not correctly reported to bbcp by the JASMIN file system.

For the full set of options, see:  https://www.slac.stanford.edu/~abh/bbcp/

Note: the "bbcp" command must be in your path on both the source and target machine. This has been arranged for you on jasmin-xfer1 but may not be the case on the machine in your own environment. You can, for example, obtain a binary distribution of the bbcp executable, or compile your own from source, and place the executable in your home directory on the remote system. You can then specify the path of the bbcp executable in the bbcp command on JASMIN, as shown in the next example.

Initiate on JASMIN: Pull Data from remote server, specifying SSH command to start bbcp

[user@jasmin-xfer1]$ bbcp -v -4 -P 5 -F --port 50000:51000 -S "/usr/bin/ssh %I -l %U %H /path/to/bbcp" username@remote-server:<PATH-TO-SOURCE-FILE> <PATH-TO-TARGET-FILE>

The path /path/to/bbcp can be replaced by module load bbcp; bbcp (or whatever is the appropriate local requirement) in environments where bbcp is a module which needs to be loaded first. For example, with dtn02.rdf.ac.uk:

[user@jasmin-xfer1]$ bbcp -v -4 -P 5 -F --port 50000:51000 -S "/usr/bin/ssh %I -l %U %H module load bbcp; bbcp" username@remove-server:<PATH-TO-SOURCE-FILE> <PATH-TO-TARGET-FILE>

For specifying the SSH command to start bbcp on the TARGET node, use the "-T" option.

The  bbcp site has good documentation on further options, including the "-r" option for recursive transfers. A number of useful tutorials are also available elsewhere on the web.

bbcp - Tuning Recommendations

We recommend you tune your connection by trying various different options on a few GBs of data.

  1. By default 4 streams are opened. Try 1 stream first, particularly on fast connections, it may be faster. This is achieved with the option -s 1.
  2. We ask users of JASMIN to tune up to a maximum of 16 streams (-s 16). If you believe you need to open more streams please contact the CEDA Helpdesk.
  3. Do not tune the window size unless you continue to get very poor bandwidth after adjusting the number of streams. Most modern operating systems will auto-tune this parameter.
  4. If you have system admin privileges on your machine you may get better bandwidth by adjusting parameters in your kernel. If you want to try this please contact the CEDA Helpdesk.
  5. bbcp is not ideal for large directory trees of small files. If you have thousands of small files you may be better off with rsync or possibly GridFTP, depending on the network

bbcp - Troubleshooting

  • bbcp uses SSH to establish the control connection so you need to set up your SSH key in the same way as you would to SSH into jasmin-xfer1.ceda.ac.uk. If bbcp isn't working you should first check you can SSH to jasmin-xfer1.ceda.ac.uk. If you can't, please review the steps in the Getting Started section before contacting the CEDA Helpdesk.
  • Make that you have logged in (via SSH) to both the JASMIN transfer server and the remote server with the -A option (agent-forwarding enabled), to ensure that your credentials are used by SSH as it invokes bbcp on the other server.
  • Try adding the -F option to disable bbcp's filesystem checking if you get the following error:
  • bbcp: Insufficient space to copy all the files from <hostname><br>
    	
  • If you see the error message "Address family not supported by protocol creating inet socket", this is most likely because the "-4" flag was not specified. This may happen with commands that once worked, as a previously installed version of bbcp on JASMIN defaulted to IPv4. Currently there is no support for IPv6 on JASMIN.

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